The present invention relates to apparatus for continuously contacting solids with liquids, and more particularly to apparatus for the efficient, step-wise contact of solid pieces, especially film chips, with at least one liquid.
In a known method silver is removed from photosensitive film by cutting the film into chips, contacting the film chips with liquid which is capable of removing the photosensitive emulsion from the chips, washing the chips with a second liquid, and recovering the silver from the first liquid and from the second, washing liquid. Apparatus developed to carry out this process has been disadvantageous and uneconomical in that the apparatus commonly performed the process on a batch basis, and upon removal of liquid from the chips or the chips from the liquid, the chips tended to stick to each other preventing efficient rinsing, or the chips tended to adhere to the vessel requiring manual removal. Additionally, inordinate quantities of washing liquid were required, which had to be treated to recover any silver, usually in the form of silver halide, which might be present in the liquid, in order for the process to be economically practiced.
An improvement in apparatus to perform the process has been disclosed in U.S. Pat. No. 4,046,154, issued Sept. 6, 1977 to Tada et al. In the improved apparatus, a pair of vertical columns having agitators and baffles are employed to permit the chips to fall by gravity through the vertical columns which are filled with liquid continuously added to the columns. The amount of film chips which can be processed in the disclosed apparatus is limited by the configuration of the apparatus and the dependency upon gravity in permitting the chips to fall or sink through the vertical contacting chambers.
As in any process in which a solid and a liquid must be contacted, and particularly where a layer must be removed from the solid, efficiency of the contacting of the liquid with the solid and subsequent rinsing of the solid becomes critically important. Even after the solid has been treated, in the particular example noted above wherein the emulsion is removed from the film and is suspended in the liquid, a quantity of liquid will adhere to the solid even after extensive draining periods. If the solid with the liquid adhering thereto is discarded, the materials in the liquid would represent a substantial economic loss to the efficiency of the process. A principal means of recovering the liquid adhering to the solid is to provide a number of rinsing operations in an attempt to reduce the amount of valuable material in the liquid adhering to the solid. Substantial rinsing requires an equally substantial quantity of rinsing liquid, ultimately requiring treatment of the liquid utilized in the rinsing operation. Even if several separate rinsing operations are employed, the volume of rinsing liquid required to be treated remains inordinate and uneconomical. Moreover, as the number of rinsing operations are increased, the volume of rinsing liquid increases significantly. Therefore, the known apparatus for contacting solids and liquids, particularly when employed in the recovery of silver from photosensitive film does not provide for the economical and efficient operation of processes for contacting and treating solids with liquids.